FILE - In this April 8, 2006 file photo, Abdul Aziz al-Hakim, the leader of the Supreme Council for the Islamic Revolution in Iraq appears at a gathering of Iraqi Shiites who were protesting the suicide bombing of a mosque in Baghdad, Iraq. Abdul-Aziz al-Hakim, the scion of a revered clerical family who channeled rising Shiite Muslim power after the fall of Saddam Hussein to become one of Iraq's most influential politicians, died Wednesday Aug. 26, 2009 in Iran, the country that was long his key ally. He was 59.(AP Photo/Karim Kadim, File)

Abdul Aziz al-Hakim, the head of Iraq's largest Shiite political party, died Wednesday, creating a leadership vacuum that could weaken the bloc ahead of the January parliamentary election.

Hakim, 59, died in Tehran, where he was being treated for lung cancer, his relatives and associates said.

Leaders of the Islamic Supreme Council of Iraq are expected to announce after Hakim's burial in Najaf this week that his son Ammar will become the new head of the party, Supreme Council officials said. However, Ammar al-Hakim, who is in his late 30s, is widely seen as too young and inexperienced to command all factions of the party, and could face a leadership challenge.

The younger Hakim has been passed over to lead a newly announced Shiite alliance, officials said. Instead, Supreme Council elder Humam Hamoudi is poised to lead the alliance, which does not include Prime Minister Nouri al-Maliki.

Iraqi officials across the political spectrum expressed sorrow Wednesday over the passing of Abdul Aziz al-Hakim, a central figure in Iraqi politics who in recent years masterfully managed to stay in the good graces of Washington as well as Tehran.

He was one of the architects of the United Iraqi Alliance, the Shiite-led coalition that won the most seats in the December 2005 parliamentary election. He was widely credited with leading Shiites to power after decades of oppression by Saddam Hussein, a Sunni.

"The man was the vital artery of the United Iraqi Alliance and the Iraqi government," said Muayed al-Hakim, a member of the extended family. "With his death, the arena is empty of a suitable figure to fill the vacuum. He had remarkable negotiating skills and a powerful, imposing personality."

Khalid al-Nimany, a member of the provincial council in Najaf, the city at the heart of Shiite politics, said Hakim's death marked a major setback for his party.

"His death came at a crucial moment, as we are slowly approaching the date for general elections and there are a lot of political stirrings, alliances being drawn and coalitions being built," Nimany said.

Hakim's passing is likely to shape al-Maliki's thinking as the prime minister decides whether to join the new Shiite alliance or form a coalition with Sunnis and possibly Kurds.

Leaders of the new Shiite coalition, which includes most of the parties that selected al-Maliki as prime minister in 2006, declined to guarantee that he would keep his job if he agreed to join the alliance. The coalition was announced Monday.

Though widely expected, Hakim's death deprives the coalition of a revered theologian known for his shrewd political and consensus-building skills.

Hakim's family emerged as one of the top threats to Hussein's regime during the 1970s. Hakim was imprisoned after a 1977 Shiite uprising and fled to Iran three years later. He was among the founders of the Supreme Council in 1982. Hakim led the party's militia, the Badr Organization, which many years later became one of the building blocks of Iraq's new army and police forces.

Hakim had battled lung cancer for years. He was treated in Houston in May 2007 and later underwent chemotherapy in Tehran.